Many telecommunications operators want to have common infrastructure for new service introduction. The so called IP Multimedia System (IMS) is a technology standardized by 3GPP. It adds the ability to deliver integrated voice and data services over the IP-based packet switched network.
The IP Multimedia System (IMS) enables a 3G system being specified by 3GPP to both benefit from the use of Internet Protocols (IPs) and offers capabilities that IP is designed to provide. These include access to Internet and multimedia content. IP offers a number of attractions over traditional telecommunications protocols: in addition to representing a bridge between the telecommunications and Internet worlds, it also offers a “seamlessness” of communication over many different types of networks. As a result, customers will experience extremely flexible telecommunications, irrespective of the various networks over which their calls may pass.
One type of service that can be even more valuable for operators and their customers is the Push-to-talk (PTT) service implemented in IMS.
Push-to-talk (PTT) is basically a “walkie-talkie” in a cellular telecommunication system. Push-to-talk systems are typically used in settings where a group of geographically diverse people require communications with each other in a “point-to-multipoint” fashion. Examples of push-to-talk system uses include workgroup communications, security communications, construction site communication, and localized military communications. The new service PTT providing group communication services is applicable to both real-time data, such as audio and video data (including voice data), and time-independent data, such as computer files, email, and so on.
Earlier known system is Land Mobile Radios, which have been used in trucks, taxis, buses, and other vehicles in order to communicate scheduling information between a central dispatch centre and one or more corresponding fleet vehicles. Communications may be directed at a specific vehicle in the fleet or to all vehicles simultaneously. These solutions are based on different technology. Another known solution based on cellular technology is the solution that the US operator Nextel has sold as a proprietary PTT-solution. This solution is called Direct Connect and is based on Motorola's iDEN (integrated Digital Enhanced Network) technology. A drawback with this solution is that their versions of the special connection calls require that all members are located in the same area served by one BSC (Base Station Controller). Another drawback is that it is not based on any standard protocols, such as RTP, and thus suffers from bandwidth problems.
WO 01/37526 discloses a general method and an apparatus for providing push to talk functionality to a conventional wireless phone. Basically, the document discloses providing an input mechanism or button that functions as a conventional telephone function while the telephone is used in conventional telephone mode, and that functions as a push to talk function while the telephone is in a push to talk mode. The document does not disclose how the telephone interacts with either a PTT-server or another telephone.
EP 0 876 072 discloses a scalable radio platform for wireless communication system which can interface with user equipment or system equipment to allow system parameters to be modified such that users of different communication systems can communicate with each other, and also allows a wireless communication system to adapt to changing radio conditions. However, the document does not disclose any pointers as to how the quality of a PTT-session between two or more subscribers with user equipment can be improved or prevented from degrading.